Remember the precocious little kid who taught us the human head weighs 8 pounds? Well, he's all grown up and has some serious muscles too! His transformation is so surprising there's no question he had to make our list. With such a buff bod, he's clearly spent less time acting and more time in the gym!

The 21-year-old hottie keep his six-pack chiseled by working free weights and circuits with his trainer four to five times per week. He also trains in Brazilian Ju Jitsu and credits an active lifestyle for his new, oh-so-hot image.

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Anna Chlumsky

Better known as: Vada Sultenfuss of My Girl

After her tear-jerking role in the memorable '90s flick, the wide-eyed sweetheart took a break from acting and went to a Lutheran high school, majored in International Studies at the University of Chicago, married a military man, and worked as a fact-checker for Zagat.

Now the stunning star is back in the spotlight and better than ever, starring opposite Julia Louis-Dreyfus in HBO's new political comedy Veep. A self-admitted nerd, the 31-year-old practices Kung Fu, enjoys Krumping in public, and stays in tip-top shape with Bikram yoga.

This childhood cutie with her trademark pigtails, adorable freckles, and fluorescent high-tops is all grown up and looking amazing! The 35-year-old actress, author, and entrepreneur balances mommyhood with running her eco-friendly clothing line, working as Target's Mommy Ambassador, and promoting her new book, Happy Chaos.

An expert in multi-tasking, Moon Frye even fits in time to exercise. She's trained with celeb fitness guru Teddy Bass (who helps her stay in shape with moves that target several muscle groups at once, so you do more in less time)—a must for ultra-busy moms like her!

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Keisha Knight Pulliam

Better known as: Rudy Huxtable of The Cosby Show

Keisha Knight Pulliam just may be the definition of child star turned Hollywood hottie! When she was only six, she was nominated for a Best Supporting Actress Emmy (and is still the youngest actress nominee in history), so we're not surprised to see her continue to heat up the small screen today.

Now starring as a reformed con artist on the TBS comedic drama Tyler Perry's House of Payne, the active actress stays in shape by practicing hot yoga, getting enough sleep, drinking plenty of water, and eating clean, organic food.

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Danica McKellar

Better known as: Winnie Cooper of The Wonder Years

America's favorite girl-next-door (and every teenage boy's fantasy) is all grown up, and wait for it— a math genius! Now a successful non-fiction author encouraging girls to have confidence in their mathematics skills, Danica McKellar recently dropped nearly all of the 40 pounds she gained during pregnancy and is rockin' one killer bod.

To get her pre-baby body back, the 37-year-old brunette beauty exercised at home with light cardio and yoga while sticking to whole grains, fresh vegetables, and organically raised chicken. The smart star also stayed away from refined sugar, dairy, and gluten. [Click to Tweet her regimen!]

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Christine Lakin

Better known as: Alicia "Al" Lambert of Step by Step

From resident tomboy to bodacious bikini babe, Christine Lakin is turning heads every step of the way! She's kept quite busy since her childhood days on Step by Step with roles on shows like 7th Heaven, 3rd Rock From the Sun, Boston Legal, CSI, and Reefer Madness.

The dynamic bombshell is known to make her workouts fun with dancing, Cardio Barre classes, hiking, Pilates, and yoga.

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Sarah Chalke

Better known as: Becky #2 of Roseanne

Although this feisty and funny female had starring roles on Scrubs, How I Met Your Mother, and Mad Love, she'll always be "second Becky" to us!

Sizzling on the small screen as Angie LeClaire in ABC's Cougar Town, Sarah Chalke keeps her figure in check by hiking with her dog, practicing yoga, and doing bootcamp-style workouts. She's also known to eat "lots of healthy stuff followed by a naughty dessert." Everything in moderation for the lovely 35 year old!

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Tatyana Ali

Better known as: Ashley Banks of The Fresh Prince of Bel-Air

Far from her days in Bel-Air, daddy's little girl has grown up to be one gorgeous woman! As busy as ever, Tatyana Ali is set as a regular on BET's upcoming comedy Second Generation Wayans. Most recently, she starred in Love That Girl for TV One and had a recurring role on The Young And The Restless.

Still sporting that signature charm and winning smile, the beautiful 33-year-old enjoys spinning, yoga, weight training, and early morning bootcamps. But the best part? She says she loves her body whether she's carrying an extra 10 pounds or not. Gotta love a gal who is healthy from the inside, out.

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Camilla Belle

Better known as: Sydney Miller of Disney Channel's Rip Girls

From pretty teenager to sophisticated vixen, former child star Camilla Belle is now a regular on the red carpet scene and style columns. The actress-turned-fashionista knows how to strike a pose but still rocks the big screen with roles in Push, 10,000 BC, Breakaway, and From Prada to Nada.

The secret to the 25-year-old's fab figure? Hatha yoga and dancing.

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Josie Davis

Better known as: Sarah Powell of Charles in Charge

We think it's safe to say Charles is no longer in charge. Josie Davis has shed her former geeky, bookish image and is now absolutely smokin'! The 39-year-old stunner is still acting with roles on Chuck, CSI, Bones, and Rules of Engagement, and has recently ventured into producing and screenwriting.

Davis credits probiotic drinks and green tea, as well as dark green salads with cucumber for keeping her figure mean and lean. Good music keeps her motivated at the gym and clearly, it works for her—those legs are amazing!

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Jonathan Lipnicki

Better known as: Renee Zellweger's son in Jerry Maguire

Remember the precocious little kid who taught us the human head weighs 8 pounds? Well, he's all grown up and has some serious muscles too! His transformation is so surprising there's no question he had to make our list. With such a buff bod, he's clearly spent less time acting and more time in the gym!

The 21-year-old hottie keep his six-pack chiseled by working free weights and circuits with his trainer four to five times per week. He also trains in Brazilian Ju Jitsu and credits an active lifestyle for his new, oh-so-hot image.

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Kelly Rowland

Better known as: Destiny's Child singer

There's a reason our fit and fabulous October cover model is such a polished professional on set—she got her start at age 11 in 1992 when she joined Beyoncé Knowles in a Houston-based singing group called Girl's Tyme, which later went on to become Destiny's Child. Their self-titled debut album was released in 1998 when she was just 17, and the rest is bootylicious history.

Today, both Kelly's career and superfit body are hotter than ever. In September 2013 she joined FOX's The X Factor as a host and she also graced the cover of SHAPE magazine, in which she shared the secrets to those amazing abs and arms. She has also released four solo studio albums since Destiny's Child. The latest, Talk a Good Game, is available now.